This invention relates to a device for suspending loads from an overlying structure, such as a ceiling or the like, in particular for lighting equipment for theaters, photographic, cinema or television studios, studios in which the trafficked surface located below the suspended equipment is used by performers and supporting staff.
The known devices, which comply with rigorous safety standards in order to prevent accidents, in particular arising from the fall of suspended loads (or a suspended load), comprise (see for example that described in Italian Utility Model application no. FI/93/U/109 lodged on the Jun. 10, 1993) a double pantograph structure and cable means to adjust the height of the load above the trafficked surface. Normally such pantograph structure terminates at the two ends in a corresponding pair of bars of appreciably shorter length in comparison with the other bars in the pantograph structure. For example the length of these terminal bars is less than one third that of the other bars, so that both the ends of such pantograph structure terminate in corresponding extension parallelograms which are appreciably reduced in size, the distal apex of which is pivoted to the overlying structure and the suspended load respectively. The apex opposite the distal apex of each of the terminal parallelograms can slide in, a corresponding vertical guide which is rigidly connected to both the overlying structure and the suspended load. In this way the system has limited rigidity in respect of transverse oscillations because of the play in the couplings between the bars in the terminal parallelograms in the vertical guides, play whose effect is amplified by the small size of the terminal bars. For these reasons known devices only permit the application of axial loads, e.g. a single lighting device whose center of gravity is vertically in line with the vertical axis of symmetry of the pantograph structure. To suspend several lighting devices as a whole without being concerned with this vertical alignment of the center of gravity of the whole, more complex and costly suspension devices (known as xe2x80x9choistsxe2x80x9d) are instead used.
Furthermore, in known devices these pantograph structures are generally suspended below a lifting winch, which may be motor-driven, which pays out/reels in suspension cables. Because of the size of the winch this fact limits the amount by which the suspended load can be moved upwards.
The purpose of this invention is to avoid these disadvantages and in particular to provide a low cost device which will also suspend eccentric loads. The invention relates to a device comprising cable lifting means for adjusting the position of loads for height and an elongatable double pantograph structure; means for attaching the device to the overlying structure and means for attaching the device to the suspended loads are provided at the opposite ends of the double pantograph structure. According to the invention, in order to limit transverse oscillations of the suspended load the connection means incorporate corresponding combined horizontal and vertical guides within which there slide corresponding pairs of terminal upper and lower bars from the systems of articulated bars, the terminal bars having a length which is similar to or only slightly less than that of the other bars in the pantograph structure. In this way, because each of the bars in such pairs of terminal bars is attached to the attachment means by means of two spaced apart pins the double bar structure has good lateral rigidity, greater than that of known devices. The guides for the pairs of upper terminal bars can be located side by side and on opposite sides of the cable lifting means so that the dimensions of the means remain contained within the elongatable structure even when the load is completely lifted and the bars in each system lie alongside each other, permitting upward travel of the suspended load which is independent of the presence of the lifting means.
In a preferred form of construction the cable lifting means comprise a motor-driven winch and the connecting means to the overlying structure comprise an upper plate below which the winch is rigidly fixed. This plate has side wings which are folded back at right angles towards the base of the opposite sides of the winch, these wings incorporating slots forming the guides in which the pairs of upper terminal bars slide.
The attachment means to the overlying structure may comprise at least one carriage equipped with at least two pairs of wheels, the pairs being spaced apart in the direction in which the carriage travels; these carriages, at least one of which may be motor-driven, are located above the plate and act to guide the device with minimum transverse play on a rail attached to the overlying structure. In this way the device and the suspended load can easily be moved horizontally along that rail, the at least two pairs of wheels spaced apart or the presence of several carriages spaced apart providing transverse rigidity against oscillations in the vertical plane passing through the rail.
The upper plate together with the corresponding side wings define an enclosure in which an electrical unit controlling the motor/reduction gear, the unit regulating the useful travel of the suspended load, and an overload and cable breakage monitoring unit can also be installed in addition to the motor/reduction gear of the winch.
In a preferred embodiment the connecting means to the suspended load located at the proximal end of the pantograph structure to the suspended load comprise a lower plate parallel to the upper plate having opposing lateral wings extending upwards at right angles in which are provided slots forming the sliding guides for corresponding pairs of lower terminal bars of the two pantograph systems. A bar which extends vertically upward, at the top end of which a rocker lever is pivoted at an intermediate point thereof to the ends of which are connected the ends of the two lifting cables operated by the winch, is attached to the center of the lower plate, at the top.
In a preferred embodiment the pivoting bar for the rocking lever extends upwards as far as is possible compatible with the available height within the device when this has all been gathered upwards. Also, in the double pantograph structure of the device, corresponding intermediate articulations between the bars in each pantograph are preferably applied to the corresponding ends of one horizontal pin which extends from one pantograph to the other, and two cable openings guiding the lifting cables of the device are attached to at least one of the pins. Both the pronounced upward development of the vertical pivot bar, which increases the mass of the part of the device suspended below the point of attachment of the lifting cables, and the presence of the cable openings for the lifting cables, effectively help to oppose lateral deformations in the attitude (namely the angular inclination of the structure with respect to some reference) of the device, in particular those due to possible differences between friction in the articulations of the pantograph.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.